Cutting inserts for groove cutting are well known in the mechanical field. FIGS. 1 and 2 show one example of a cutting insert used for groove cutting. Referring to FIGS. 1 and 2, a cutting insert 5 has a first cutting portion 6, a second cutting portion 7 and a mounting portion 8. The first cutting portion 6 and the second cutting portion 7 are located on an upper face of the cutting insert 5 at respective longitudinal ends of the cutting insert 5. The first and second cutting portions 6 and 7 are mirror-symmetrical to each other about a center line C. Thus, a width Wa of an end of the first cutting portion 6 is equal to a width Wb of an end of the second cutting portion 7. The mounting portion 8 is higher than the first and second cutting portions 6 and 7 to prevent the first cutting portion 6 and the second cutting portion 7 from contacting a tool holder when mounting the cutting insert 5 to the tool holder. That is, a height Hb of the mounting portion 8 is greater than heights Ha of the first and second cutting portions 6 and 7. The mounting portion 8 has a mounting groove 9 formed in a longitudinal direction of the mounting portion 8. The mounting groove 9 engages a mounting protrusion of the tool holder.
FIG. 3 shows another example of a cutting insert used for groove cutting. FIG. 4 shows that the cutting insert shown in FIG. 3 is mounted to a tool holder. Referring to FIG. 3, the cutting insert 1 includes a body 10, which is centrally located, and first and second cutting portions 20 and 30, which are located at longitudinal ends of the body 10 respectively and have a substantially identical shape. The first cutting portion 20 and the second cutting portion 30 are located in different faces of the cutting insert 1. The body 10 has a first upper mounting surface 11, a second upper mounting surface 12 adjacent to the first upper mounting surface 11, a first lower mounting surface 13 opposite to the first upper mounting surface 11, and a second lower mounting surface 14 opposite to the second upper mounting surface 12. The first and second upper mounting surfaces 11 and 12 have receiving grooves 15 and 16, respectively. The receiving groove 15 is formed on the first upper mounting surface 11 in a width direction of the first upper mounting surface 11 and the receiving groove 16 is formed on the second upper mounting surface 12 in a width direction of the second upper mounting surface 12. Referring to FIG. 4, the cutting insert 1 is mounted to a tool holder 40 in an insert insertion direction shown in FIG. 4 (i.e., from a lateral surface of the tool holder 40). An upper support surface of the tool holder 40 engages the receiving groove 15 of the cutting insert 1 and a stopper formed on a lower support surface of the tool holder 40 engages a recess formed on the first lower mounting surface 13 of the cutting insert 1. When cutting a workpiece, a force applied to the cutting insert 1 in the longitudinal directions L1 and L2 is supported by the engagement between the receiving groove 15 and the upper support surface of the tool holder 40, while a force applied to the cutting insert 1 in the width directions W1 is supported by the engagement between the recess of the first lower mounting surface 13 and the stopper of the tool holder 40.